Everything is included at CSS no matter where you book, so don't let the website give the impression that they are the ones giving you a deal. It could be a legit site, so if you feel comfortable with it, go for it.

We used to book via an online travel site, but now we book directly with Couples. It gives us piece of mind in case anything were to go wrong we have a direct line to the resort. Plus Couples will match any legitimate price so we always get the best deal.

Define "everything included"... When Couples says All-Inclusive, they mean All-Inclusive, and it makes no difference if you book through your local brick-and-mortar TA, an on-line TA, or directly through Couples.

I would be wary of any TA that claims they are offering you something more than what Couples already offers, unless its an off-site excursion (other than the Cat Cruise, snorkel tours, glass bottom boat tours, etc.)... Check the Couples website for their standard all-inclusives before falling for any extras that a TA offers as unique in their package.